Semiconductor device and method for forming the same

ABSTRACT

A semiconductor device is made up of a semiconductor substrate with an active region, an oxide film to cover the active region of the semiconductor substrate, a first borophosphosilicate glass film to cover the oxide film, and a second borophosphosilicate glass film to cover the first insulating film. Wherein the first borophosphosilicate glass film has a concentration of a boron which is lower than that of the second borophosphosilicate glass film. Accordingly, the semiconductor device can avoid can give an outdiffusion preventing function to an underlayer for phosphorus of plural interlayer insulators including boron.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention:

[0002] The present invention generally relates to a semiconductor deviceand a method for forming the same, and more particularly, the presentinvention relates to the semiconductor device and the method for formingthe same, having a borophosphosilicate glass film as an interlayerinsulator.

[0003] This application is a counterpart of Japanese application SerialNumber155220/1998, filed May 20, 1998, the subject matter of which isincorporated herein by reference.

[0004] 2. Description of the Related Art: In general, a multi-levelinterconnection is used effectively to advantage a high integration. Inthe multi-level interconnection, an interlayer insulator is formedbetween interconnections. A borophosphosilicate glass film as theinterlayer insulator is used for planarization in VLSI circuit.

[0005] The borophosphosilicate glass film covers an active region of asemiconductor device such as a MOS transistor. After then, theborophosphosilicate glass film is reflew using thermal treatment. As aresult, the interlayer insulator having a smooth surface is formed.

[0006] However, phosphorus in the borophosphosilicate glass film arediffused to the active region of the semiconductor device during reflow.It is desirable to avoid the outdiffusion of the phosphorus to theactive region of the semiconductor device.

SUMMARY OF THE INVENTION

[0007] An object of the present invention is to provide a semiconductordevice that can give an outdiffusion preventing function to anunderlayer for phosphorus of plural interlayer insulators includingboron.

[0008] According to one aspect of the present invention, for achievingthe above object, there is provided a semiconductor device comprising: asemiconductor substrate with an active region; an oxide film to coverthe active region of the semiconductor substrate; a firstborophosphosilicate glass film to cover the oxide film; and a secondborophosphosilicate glass film to cover the first insulating film;wherein the first borophosphosilicate glass film has a concentration ofa boron which is lower than that of the second borophosphosilicate glassfilm.

[0009] An object of the present invention is to provide a method forforming a semiconductor device that can avoid the outdiffusion of thephosphorus to the active region of the semiconductor device.

[0010] According to another aspect of the present invention, forachieving the above object, there is provided a method for forming asemiconductor device comprising:

[0011] providing a semiconductor substrate with an active region;covering the active region of the semiconductor substrate with an oxidefilm; covering the oxide film with a first borophosphosilicate glassfilm having an inhibitory of an outdiffusion of the phosphorus; coveringthe first borophosphosilicate glass film with a secondborophosphosilicate glass film including a phosphorus and a boron; andreflowing the second borophosphosilicate glass film so as to have afluidity with thermal treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] While the specification concludes claims particularly pointingout and distinctly claiming the subject matter that is regarded as theinvention, the invention, along with the objects, features, andadvantages thereof, will be better understood from the followingdescription taken in connection with the accompanying drawings, inwhich:

[0013]Fig. 1A-Fig.1D are sectional views showing a method for forming asemiconductor device according to a first preferred embodiment of apresent invention.

[0014]FIG. 2 is a sectional view showing a method for forming asemiconductor device according to a second preferred embodiment of apresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A semiconductor device according to first and second preferredembodiments of the present invention will hereinafter be described indetail with reference to the accompanying drawings.

[0016]Fig. 1A-Fig. 1D are sectional views showing a method for forming asemiconductor device according to a first preferred embodiment of apresent invention. Here, for example, the semiconductor device is DRAM(Dynamic Random Access Memory) having a COB(Capacitor On Bit line)structure.

[0017] As shown in FIG. 1A, a field oxide film 11, preferably to athickness of about 400 nm, is formed on a surface of a semiconductorsubstrate 10 as a silicon, using LOCOS (LOCal Oxidation of Silicon)method. The field oxide film 11 serves as an isolation betweentransistors. By forming the field oxide film 11 on the surface of thesemiconductor substrate 10, an active region is defined on the surfaceof the semiconductor substrate 10. A gate oxide film, preferably to athickness of 50-150Å, is formed on the active region of a semiconductorsubstrate 10. A gate 14, preferably to a thickness of 2000-4000Å, ismade up of a polysilicon layer 15 and a tungsten silicide layer 16. Aninsulating layer 17, preferably to a thickness of 2000-3000Å, is made upof an NSG (Non doped Silicate Glass) film or a PSG (Phosphorus dopedSilicate Glass) film formed on the gate 14 using CVD techniques. Asidewall spacer 18 is made up of an NSG film or a PSG film formed on asidewall of the gate 14. A diffused region is formed on the activeregion between gates 14 using ion-implantation technique. An oxide film20, preferably to a thickness of 200-500Å, is formed on the activeregion to avoid damages of the active region before the ionimplantation. In a DRAM, a select transistor and a memory cell capacitorare formed on the active region 12 between gates 14. A silicon nitridefilm is deposited using low pressure chemical vapor deposition and thenthe silicon nitride film is patterned, so as to cover the gate 14, thesidewall spacer 18 and the oxide film 20 on the active region. As aresult, the patterned silicon nitride serves as a sacrificial film 21.The sacrificial film 21 is formed on a region which forms a bit contact.A first borophosphosilicate glass film 22, preferably to a thickness of1000-2000Å, is formed on the sacrificial film 21 and on exposed portionsfrom the sacrificial film 21 using CVD method. The firstborophosphosilicate glass film 22 serves as a first interlayerinsulator. A concentration of a boron oxide in the firstborophosphosilicate glass film 22 is 10-12 weight %. A concentration ofphosphorus (P205) in the first borophosphosilicate glass film 22 is10-15 weight %.

[0018] A second borophosphosilicate glass film 23, preferably to athickness of 3000-5000Å, is formed on the first borophosphosilicateglass film 22 using CVD method. The second borophosphosilicate glassfilm 23 serves as a second interlayer insulator. A concentration of aboron oxide in the second borophosphosilicate glass film 23 is 12-18weight % which is higher than that of the first borophosphosilicateglass film 22. A concentration of phosphorus (P205) in the secondborophosphosilicate glass film 23 is 10-15 weight % which issubstantially same as that of the first borophosphosilicate glass film22.

[0019] After depositing the first and second borophosphosilicate glassfilms 22, 23, the entire structure is annealed for reflow in N2atmosphere at 800-950° C. As a result, a surface of the secondborophosphosilicate glass film 23 become smooth. In this time,phosphorus in the first and second borophosphosilicate glass films 22,23 intend to diffuse the diffused regions 19 under the first and secondborophosphosilicate glass films 22, 23 via the oxide film 20. However,the first preferred embodiment has the interlayer insulators of twolayers which is made up of the first and second borophosphosilicateglass films 22, 23. Further, the first borophosphosilicate glass films22 directly covering the oxide film 20 on the active region 12, whichhas the concentration of the boron oxide which is lower than the secondborophosphosilicate glass film 23. In a borophosphosilicate glass filmincluding phosphorus and boron, it is well known that diffusioncoefficient of the phosphorus is in proportion to the concentration ofthe boron. Therefore, the phosphorus diffusion coefficient of the firstborophosphosilicate glass films 22 having the concentration of thephosphorus which is lower than the concentration of the boron in thesecond borophosphosilicate glass film 23, which is smaller than that ofthe second borophosphosilicate glass film 23. Accordingly, the firstinterlayer insulator 22 located between the second interlayer insulator23 and the oxide film 20, which serves as a phosphorus diffusionpreventing film against the second interlayer insulator 23. By formingthe first interlayer insulator 22 as the phosphorus diffusion preventingfilm, it can prevent to diffuse from the second borophosphosilicateglass film 23 to the active region 12 via the oxide film 20.Accordingly, a contamination of the active region 12 caused by thephosphorus, which can avoid.

[0020] As shown in Fig. 1C, after a reflow treatment of the first andsecond borophosphosilicate glass films 22, 23, a contact hole 24 isformed in the first and second borophosphosilicate glass films 22, 23which is not cover with the sacrificial film 21 and which locates on thediffused region 19, using a well-known photolithography and etchingtechniques. In etching for forming the contact hole, C4F8 gas is used.As a result, etch rate of the borophosphosilicate glass film increaseswith decrease of the concentration of boron.

[0021] Therefore, a phenomenon of etching stop easily appears in thefirst borophosphosilicate glass films 22, but the firstborophosphosilicate glass films 22 has the etch rate which is largerthan the second borophosphosilicate glass films 23. Accordingly, thecontact hole 24 can preferably form.

[0022] After forming the contact hole 24, a bit line 25 is formed so asto contact to the diffused region 19 via the contact hole 24. Afterthen, as shown in Fig. ID, an interlayer insulator 26 is formed on thebit line 25. The interlayer insulator 26 is formed using the similarmanner for the second borophosphosilicate glass films 23.

[0023] After forming the interlayer insulator 26, for forming a memorycapacitor, a cell contact 27 is formed in the interlayer insulator 26,the first and second borophosphosilicate glass films 22, 23, and thesacrificial film 21, using first and second dry etching. Next, a storageelectrode 28 which is made up of a doped-polysilicon, is formed in thecell contact 27. A dielectric film 29 is formed on the storage electrode28. A cell plate 30 is formed on the dielectric film 29. As a result,the memory capacitor is made up of the storage electrode 28, thedielectric film 29, and the cell plate 30.

[0024] In the dry etching, since the first borophosphosilicate glassfilm 22 has a concentration of boron oxide which is lower than thesecond borophosphosilicate glass film 23, the first borophosphosilicateglass film 22 has an etch rate which is higher than the secondborophosphosilicate glass film 23. Therefore, before erosion for ashoulder portion 21b of the sacrificial film 21 in the first dryetching, a bottom portion 21 a of the sacrificial film 21 can expose.Accordingly, a damage of the sidewall spacer 18 in the second dryetching caused by the erosion for the shoulder portion 21 b of thesacrificial film 21, can avoid. it can avoid that the gate 14 shortswith the storage electrode 28. Further, the first preferred embodimentcan give an outdiffusion preventing function to an underlayer forphosphorus of plural interlayer insulators including boron.

[0025]FIG. 2 is a sectional view showing a semiconductor deviceaccording to a second preferred embodiment of a present invention;

[0026] As shown in FIG. 2, a field oxide film 11 is formed so as tosurround a diffused region 19 on a semiconductor substrate 10. An oxidefilm 20 is formed on the diffused region 19. The oxide film 20 iscovered with a first borophosphosilicate glass film 22. A secondborophosphosilicate glass film 23 is formed on the firstborophosphosilicate glass film 22. A cell plate 30 is formed on thesecond borophosphosilicate glass film 23. An interlayer insulator 26,preferably to a thickness of 4000-8000Å, covers the cell plate 30. In afirst contact hole 33 to the cell plate 30 via the interlayer insulator26 and a second contact hole 34 to the diffused region 19 via theinterlayer insulator 26, the first and second borophosphosilicate glassfilms 22, 23, and the oxide film 20, the first contact hole 33 has adifferent depth from the second contact hole 34. The firstborophosphosilicate glass film 22 has an etch rate which is faster thanthe second borophosphosilicate glass film 23. Accordingly, the first andsecond contact holes having a different depth can form, simultaneously,without damaging the cell plate.

[0027] While the present invention has been described with reference tothe illustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments of the invention, will beapparent to those skilled in the art on reference to this description.It is therefore contemplated that the appended claims will cover anysuch modifications or embodiments as fall within the true scope of theinvention.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor substrate with an active region; an oxide film to coverthe active region of the semiconductor substrate; a firstborophosphosilicate glass film to cover the oxide film; and a secondborophosphosilicate glass film to cover the first insulating film;wherein the first borophosphosilicate glass film has a concentration ofa boron which is lower than that of the second borophosphosilicate glassfilm.
 2. A semiconductor device as claimed in claim 1, wherein aconcentration of a boron oxide in the first borophosphosilicate is 10-12weight %, and a concentration of a boron oxide in the secondborophosphosilicate glass film is 12-18 weight %.
 3. A semiconductordevice as claimed in claim 1, wherein the first borophosphosilicateglass film is a phosphosilicate glass film.
 4. A semiconductor device asclaimed in claim 1, wherein the first borophosphosilicate glass film isa silicate glass film.
 5. A method for forming a semiconductor devicecomprising: providing a semiconductor substrate with an active region;covering the active region of the semiconductor substrate with an oxidefilm; covering the oxide film with a first borophosphosilicate glassfilm having an inhibitory of an outdiffusion of the phosphorus; coveringthe first borophosphosilicate glass film with a secondborophosphosilicate glass film including a phosphorus and a boron; andreflowing the second borophosphosilicate glass film so as to have afluidity with a thermal treatment.
 6. A method for forming asemiconductor device as claimed in claim 5, wherein a concentration of aboron oxide in the first borophosphosilicate is 10-12 weight % and aconcentration of a boron oxide in the second borophosphosilicate glassfilm is 12-18 weight %.
 7. A method for forming a semiconductor deviceas claimed in claim 5, wherein the first borophosphosilicate glass filmis a phosphosilicate glass film.
 8. A method for forming a semiconductordevice as claimed in claim 5, wherein the first borophosphosilicateglass film is a silicate glass film.